A method for measurement of electrophysical properties of delta-doped diamond samples loaded into the measurement cell based on symmetrical stripline is demonstrated. The simulation of S-parameters of the measurement cell with doped diamond samples is carried out. The influence of the carrier density on the transmission characteristics of the symmetric stripline with doped diamond film is investigated. An increase of the carrier density in the doped diamond film from 5•10¹⁹ m^-3 to 10²² m^-3 leads to frequency shift of transmission characteristic minimum from 15.85 GHz to 16 GHz and increasing of incretion losses from -15 dB to -25 dB.